It is widely believed that the placenta is a completely sterile organ from which a fetus gains the oxygen and nutrients it needs. But new research from the Baylor College of Medicine in Houston, TX, may quash this theory; investigators found that the placenta harbors bacteria that could have implications for pregnancy.

For their study, recently published in the journal Science Translational Medicine, the research team analyzed placenta samples from 320 subjects.

The samples underwent a process called shotgun metagenomic sequencing, which allowed the team to closely assess the diversity of bacteria in the placenta, as well as identify specific microbes and their genetic pathway.

Explaining the reasons behind conducting this research, lead study author Dr. Kjersti Aagaard, associate professor of obstetrics and gynecology in the section of maternal fetal medicine at Baylor and the Texas Children's Pavilion for women, says:

"After we completed our studies of the vaginal microbiome (the population of microbes - bacteria, viruses and fungi - that live in human cells) in pregnancy, we noted that the most abundant microbes in the mom's vagina were not what populated the baby's intestinal microbiome."

"We reasoned that there must be another source 'seeding' the infant's gut at birth, so we sought to examine the placenta," she adds.

Bacteria in placenta 'similar to bacteria found in the mouth'

After analyzing the samples, the researchers found that there are low but diverse bacteria present in the placenta, suggesting it is not as sterile as previously thought.

Researchers found that E. coli was the most common bacteria in the placenta.

The team found that the bacteria Escherichia coli (E. coli) were most common among samples. These bacteria usually reside in the intestines of healthy individuals.

Perhaps most interestingly, the researchers found that the bacteria Prevotella tannerae and Neisseria were very common among samples. These are bacteria usually found in oral cavities.

On comparing the placenta microbiome with other body sites, the team found that it was most similar to the oral microbiome rather than sites nearby, such as the vaginal or intestinal microbiomes.

Dr. Aagaard says this particular finding indicates that bacteria in the placenta may have implications for oral health during pregnancy. "It reinforces long-standing data relating periodontal disease to risk of preterm birth," she adds.

Preterm birth and infection 'influences placental microbiome'

The team also found that samples from subjects who experienced infection during pregnancy - such as urinary tract infections - showed differences in their placental microbiome, even when their infection was successfully treated with antibiotics months before.

In addition, samples from subjects who experienced a preterm birth also showed differences in their placental microbiome.

Based on this finding, the researchers note that fetus exposure to a placental microbiome may influence development throughout pregnancy and in early life. But they say that further research is needed to find out more.

As such, the team is in the process of conducting a larger study to determine the placental microbiomes throughout all stages of pregnancy, particularly among women who are at risk of experiencing preterm birth.

"These discoveries could lead to rapid breakthroughs in not only identifying women at risk for preterm birth, but developing new and worthwhile strategies to prevent preterm birth," says Dr. Aagaard, adding:

"As we catch glimmers of the microbial biology of pregnancy, we can start to see a not-too-distant future where we will prevent preterm birth (or its complications in newborns) with truly novel approaches aimed at enhancing the healthy microbes of not just the vagina, but the mouth and gut.

As we unravel the mysteries of pregnancy, we are learning that our microbes may be as much friend as foe. That is fantastic news for our moms and their babies."

Earlier this year, Medical News Today reported on a study published in PLOS ONE, which suggested that bacteria residing on the walls of the water sac that protects the baby during pregnancy may be a cause of preterm birth.

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